Effect of short-term prescription opioids on DNA methylation of the OPRM1 promoter

Background Long-term opioid use has been associated with hypermethylation of the opioid receptor mu 1 (OPRM1) promoter. Very little is currently known about the early epigenetic response to therapeutic opioids. Here we examine whether we can detect a similar increase in DNA methylation in the days following the use of prescribed opioids. Longitudinal changes in DNA methylation was assayed using the Illumina Infinium Human MethylationEPIC array in a cohort of 33 opioid-naïve participants who underwent standard dental surgery followed by opioid medication self-administration. Saliva samples were collected before surgery (visit 1), and at two postsurgery visits at 2.7 ± 1.5 days (visit 2), and 39 ± 10 days (visit 3) after the discontinuation of opioid analgesics.

Results The perioperative methylome underwent significant changes over the three visits. This was unrelated to opioids, and primarily due to postoperative inflammatory response and alteration in cellular composition. Deconvolution of cell heterogeneity indicated an increase in granulocytes at visit 2 and compensatory decline by visit 3. To specifically examine the effect of opioids, we applied a candidate gene approach and evaluated 10 CpGs located in the OPRM1 promoter. There was significant cross-sectional variability in opioid use, and for participants who self-administered the prescribed drugs, the total dosage ranged from 5–210 morphine milligram equivalent (MME). Participants were categorized by cumulative dosage into three groups: <25 MME, 25–90 MME, ≥90 MME. Using mixed effects modeling, 4 CpGs had significant positive associations with opioid dose at 2-talied p-value < 0.05, and overall, 9 of the 10 CpGs showed the predicted higher methylation in the higher dose groups relative to the lowest dose group. After adjustment for age and cellular heterogeneity, the promoter mean methylation also had positive associations with cumulative MME (regression coefficient = 0.0002, 1-tailed p-value = 0.02), and duration of opioid use (regression coefficient = 0.003, 1-tailed p-value = 0.001), but this effect was significant only for visit 3.

Conclusion The present study provides evidence that the hypermethylation of the OPRM1 promoter is in response to opioid use, and such epigenetic restructuring can be induced even by short-term use of therapeutic opioids.